GB2216506A

GB2216506A - Hollow articles

Info

Publication number: GB2216506A
Application number: GB8905203A
Authority: GB
Inventors: Stephen Roy Loomes
Original assignee: BXL Plastics Ltd
Current assignee: BXL Plastics Ltd
Priority date: 1988-03-08
Filing date: 1989-03-07
Publication date: 1989-10-11
Anticipated expiration: 2009-03-07
Also published as: GB2216506B; GB8905203D0; GB8805450D0

Abstract

In a moulded hollow article 1, such as a bottle closure, having an end wall 2 and a side wall 4 at least a part of the side wall is interrupted along at least one line 8 extending from a free end of the side wall and at least part way towards the end wall. Preferably the article is moulded using cooperating female and core moulds, the female and/or the core mould having at least one upstanding component and the moulding surface(s) to produce the line 8, which permits the side wall to be flexed to assist in separation of the core mould and article. <IMAGE>

Description

HOLLOW ARTICLES This invention relates to a method for the production of hollow articles, particularly of the type that is moulded on a mould core from which it has to be subsequently separated. The invention also relates to articles produced by the method and to apparatus for use in the method.

The separation of a hollow article of the above type moulded from, for example, a flowable material such as a thermoplastics material, can be difficult and in some cases impossible without causing damage to the mould core or to the moulded article, particularly when the internal surface of the latter has any reduction occurring in a dimension transverse to the axis extending in the direction along which relative movement of the core from said article is required to effect separation.

This difficulty may be overcome by the use of rubbery moulding materials permitting the moulded article to be stretched during separation from the core. Another means is to #employ a destructible or collapsible core.

Rubbery materials are not always suitable for the hollow article in its end use application, destructible cores are largely inconvenient to use and collapsible cores are, of necessity, complex in design and operation and therefore expensive to produce and maintain.

We have now devised a method for the production of moulded hollow articles whereby separation of the moulded article from the mould core may be facilitated while adding little to the cost of the mould.

Accordingly, the present invention is a moulded hollow article having an end wall and a side wall characterised in that the continuity of at least a part of the side wall is interrupted along at least one line extending from a free end of the side wall and at least part way towards said end wall to thereby increase the flexibility of said side wall.

In the hollow article, the interruption in the side wall is suitably produced simultaneously with the formation of the side wall and said interruption preferably extends throughout the thickness of the side wall.

In the hollow article the internal surface of the side wall suitably has a reduction occurring in dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall whereby the smaller dimension is closer to the free end of the side wall.

The hollow article suitably comprises an injection moulded or compression moulded plastics bottle closure wherein the said side wall comprises an inner annular skirt for insertion into the mouth of a bottle.

In this case the external diameter of the skirt reduces towards the free end of the side wall. Also, the internal and external diameters of the skirt reduce linearly over the major portion of the skirt length and then reduce progressively to provide the skirt with an in-turned end.

According to a further embodiment of the present invention there is provided a method for the production of a moulded hollow article having an end wall and a side wall, on a mould core characterised in that during moulding the continuity of at least a part of the side wall is interrupted along at least one line extending from a free end of the side wall and at least part way towards said end wall thereby permitting the side wall to be flexed adequately after moulding to facilitate separation of the core and atricle.

The hollow article produced by the method of the present invention may be any hollow article having an end wall and a side wall moulded from a material which can be flexed at least to a small extent. However, the method is particularly advantageous when used according to a preferred embodiment directed to the moulding of such hollow articles wherein the internal surface of the side wall has a reduction occurring in a dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall and along which relative movement of the core and the moulded article is required to effect separation, whereby the small dimension is close to the free end of the side wall.

The end wall of the hollow article of this invention may be a continuous wall or a non-continuous wall. In the latter case the wall may, for example, have one or more openings and may, for example, comprise a perforate or mesh-like structure.

The method of the preferred embodiment has been found to be particularly advantageous when used in the production of bottle closures of the type having an inner skirt which is intended to enter the mouth of a bottle and assist the formation of a mechanical seal between the closure and bottle mouth. Closures of this type have commonly been produced with a tapered inner skirt to facilitate insertion of the closure into the bottle mouth. The taper has invariably been such that the outside diameter of the skirt reduces as the distance from the end wall increases, with the inner diameter of the skirt remaining substantially constant.

Because the angle of the external taper of the skirt frequently cannot be altered to any large extent, for reasons of maintaining efficiency in its end use application, any lengthening of the skirt that-might be desired has been accomplished by increasing the thickness of the skirt at the widest part of the taper. This expedient however is frequently unsatisfactory since a point is often reached when the required thickness of material is such that, in the moulding of such closures, sink marks occur which adversely affect the formation of a satisfactory seal with the bottle mouth.

A solution to this problem has been found in designing the skirt such that its inner diameter decreases also with distance from the end wall. In this way, the range of skirt lengths for a given skirt thickness at its widest point and external taper may be extended via the freedom to alter the internal taper to suit requirements.

The greater freedom of skirt design permitted by the above solution clearly allows the taper to be extended in length with retention of the external taper angle or, if desired, with an increase in the external taper angle, which may be progressive, thereby to provide the skirt with an in-turned free end.

This latter feature may be desired to improve the ease with which a bottle mouth may be located during application of a closure. It will be appreciated that in providing an in-turned skirt both the external and internal diameters of the skirt may each be reduced at a progressively greater rate beyond an initial external taper.

Closures with such skirt modifications would be difficult to separate from core moulds used in conventional moulding processes not employing collapsible or destructable mould cores. Because of the vast numbers of such closures that are required to be produced for the bottling industry and the large numbers of moulds therefore to be employed, the use of such latter expedients could not normally be contemplated. Accordingly, the method of the present invention is particularly advantageous for the production of such closures and other hollow articles incurring similar mould separation difficulties.

The interruption of the continuity of the side wall of the article during moulding according to the method of this invention may be effected by incorporating a mould component, which may be fixed or retractable, on the female and/or on the core mould whereby during moulding the moulding material is divided.

Preferably, the said component is provided on the female mould whereby it may constitute no significant interference with the separation of the core and the moulded article.

It is preferred that the mould component or components are such that the interruption of the side wall extends throughout its thickness. One or more of said mould components may be incorporated to provide one or more interruptions which may be linear or curved.

While the moulding material may be moulded by an injection moulding process, other processes such as compression and thermoforming processes may be employed.

The moulding materials that may be used in the method of this invention should be such that the degree of flexing of the side wall permitted by the moulded interruption, will allow separation of the core from the moulded article. While the choice of material will be determined to some extent by the dimensions of the side wall and of the interruption, materials such as plasticised polyvinyl chloride, polyolefins including high, medium or low density polyethylene and polypropylene may be employed as may some more rigid materials although it is preferable that these are not brittle. In this connection, polystyrene and methyl methacrylate polymers for example, are preferably used in a toughened form.It is envisaged that thermosetting materials might also be employed and particularly where post-mould curing might be employed to overcome any serious brittleness problem with the cured material.

The apparatus of this invention comprises a composite mould comprising a female mould and a cooperating core mould for the moulding of a hollow article having an end wall and a side wall, characterised in that the female and/or the core mould has at its moulding surface at least one upstanding component extending from the end of the composite mould corresponding to a free end of the side wall of the hollow article and at least part way towards the end of the composite mould corresponding to the end wall of the hollow article, to interrupt the continuity of at least a part of the side wall of the article and preferably throughout the thickness of the side wall.

In apparatus according to a preferred embodiment of this invention, the female mould and cooperating core mould are for the moulding of a hollow article having an end wall and a side wall wherein the internal surface of the side wall has a reduction occurring in a dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall and along which relative movement of the core and the moulded article is required to effect separation whereby the smaller dimension is closer to the free end of the side wall The production of a hollow moulded article according to the present invention will now be described but it should be appreciated that the description is given by way of illustration only and is not to be construed as limiting the scope of the present invention.

Figure 1 illustrates a hollow article comprising a moulded plastic closure with a captive over-closure, suitable for use on for example a liquid detergent or like bottle.

Figure 2 shows an enlarged part cross-section of the closure of Figure 1.

This closure indicated generally by 1 moulded from, for example, low density polyethylene thermoplastics material comprises an end wall 2 an external annular skirt 3 and internal annular skirt comprising a side wall 4 for cooperating in sealing engagement respectively with the external and internal surfaces of the neck of a bottle when fitted to the bottle mouth. Annular ribs 5 and 6 which can cooperate with corresponding annular recesses on the bottle neck provide a means of securing the closure to the bottle.

The internal annular skirt comprising side wall 4 has an external diameter which, with the exception of the rib region, reduces linearly with distance from the end wall 2 over a major proportion of its length. Near the free end of the side wall its external diameter reduces at a progressively greater rate to provide the side wall with an in-turned end. Similarly the internal diameter of side wall 4 reduces linearly with distance from the end wall 2 over a major proportion of its length and then at a progressively greater rate to provide the side wall with a tapering cross-section overall.

Side wall 4 is provided with interruption 8 extending throughout the thickness of the side wall whereby the side wall is provided with greater flexibility.

Closure 1 is produced employing a splittable female mould and cooperating core mould between which is injected molten thermoplastics material in known manner.

In the region corresponding to the free end of the inner skirt, the female mould has on its surface an upstanding rib which is narrow in relation the inner skirt circumference and has a length extending about one half of the distance from said free end to the mould portion corresponding to the end wall of the closure, the rib being so dimensioned as to make sealing engagement along its length with the core mould whereby interruption 8 in the form of a linear slot may be moulded into the side wall comprising the inner skirt.

After the molten thermoplastic has been injected into the mould assembly and has been allowed to cool, the female mould is split and removed leaving the moulded closure on the mould core. The flexibility imparted to the side wall by the moulded interruption then permits the moulded closure to be stripped from the mould core despite the unfavourable reverse taper and inturned mould surface of the core mould.

It will be appreciated that instead of a single rib, two or more ribs may be provided and their shape and length may be varied considerably.

Other possible variations within the scope of the present invention will be evident to the skilled addressee having now described the invention.

Claims

Claims:

1. A moulded hollow article having an end wall and a side wall characterised in that the continuity of at least a part of the side wall is interrupted along at least one line extending from a free end of the side wall and at least part way towards said end wall to thereby increase the flexibility of said side wall.

2. A hollow article according to claim 1 wherein the interruption in the side wall has been produced simultaneously with the formation of the side wall.

3. A hollow article according to either claim 1 or claim 2 wherein said interruption extends throughout the thickness of the side wall.

4. A hollow article as claimed in any one of the previous claims wherein the internal surface of the side wall has a reduction occurring in a dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall whereby the smaller dimension is closer to the free end of the side wall.

5. A hollow article as claimed in any one of the previous claims comprising an injection moulded or compression moulded plastics bottle closure wherein the said side wall comprises an inner annular skirt for insertion into the mouth of a bottle.

6. A hollow article as claimed in claim 5 wherein the external diameter of the skirt reduces towards the free end of the side wall.

7. A hollow article as claimed in claim 6 wherein the internal and external diameters of the skirt reduce linearly over the major portion of the skirt length and then reduce progressively to provide the skirt with an in-turned end.

8. A hollow article substantially as described herein.

9. A method for the production of a moulded hollow article having an end wall and a side wall on a mould core characterised in that during moulding the continuity of at least a part of the side wall is interrupted along at least one line extending from a free end of the side wall and at least part way towards said end wall to thereby permit the side wall to be flexed adequately after moulding to facilitate separation of the core mould and the article and after moulding flexing said side wall adequately to assist the separation of said core and said article.

10. A method as claimed in claim 9 wherein the said interruption extends throughout the thickness of the side wall.

11. A method as claimed in either claim 9 or claim 10 wherein the internal surface of the side wall has a reduction occurring in a dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall and along which relative movement of the core and moulded article occurs in effecting their separation whereby the smaller dimension is closer to the free end of the side wall.

12. A method as claimed in any one of claims 9 to 11 wherein the moulding is compression or injection moulding.

13. A method as claimed in any one of claims 9 to 12 wherein the hollow article is a moulded plastics bottle closure and said side wall comprises an inner annular skirt for insertion into the bottle mouth.

14. A method as claimed in claim 13 wherein the external skirt diameter reduces towards the free end of the side wall.

15. A method as claimed in claim 14 wherein the internal and external diameters of the skirt reduce linearly over the major portion of the skirt length and then reduce progressively to provide the skirt with an in-turned end.

16. A method substantially as described herein.

17. Apparatus comprising a composite mould comprising a female mould and a cooperating core mould for the moulding of a hollow article having an end wall and a side wall, characterised in that the female and/or the core mould has at its moulding surface at least one upstanding component extending from the end of the composite mould corresponding to a free end of the side wall of the hollow article and at least part way towards the end of the composite mould corresponding to the end wall of the hollow article to interrupt the continuity of at least a part of the side wall.

18. Apparatus as claimed in claim 17 wherein the upstanding component is provided on the female mould which is a splittable mould.

19. Apparatus as claimed in claim 18 wherein the core mould contacts the upstanding component along substantially the whole length of the upstanding component when the female and core moulds are in cooperating relationship.

20. Apparatus as claimed in any one of claims 17 to 19 which is for injection or compression moulding of the hollow article.

21. Apparatus as claimed in any one of claims 17 to 20 wherein the female mould and core mould are for the moulding of a hollow article having an end wall and a side wall wherein the internal surface of the side wall has a reduction occurring in a dimension transverse to the axis extending in the direction from the end wall towards the free end of the side wall and along which relative movement of the core and the moulded article is required to effect their separation whereby the smaller dimension is closer to the free end of the side wall.

22. Apparatus comprising a composite mould comprising a female mould and a cooperating core mould for the moulding of a hollow article as claimed in any one of claims 1 to 8.